IMAGE  EVALUATION 
TEST  TARGET  (MT-3) 


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Photographic 

Sciences 

Corporation 


23  WEST  MAIN  STREET 

WEBSTER,  N.Y.  14580 

(716)872-4503 


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CIHM/ICMH 

Microfiche 

Series. 


CIHM/ICMH 
Collection  de 
microfiches. 


Canadian  Institute  for  Historical  Microreproductions  /  Institut  Canadian  de  microreproductions  historiques 


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.^g 


.-c^ 


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Tachnical  and  Bibliographic  Notaa/Nota*  tachniquaa  at  bibliographiquaa 


Tha  inatituta  haa  attamptad  to  obtain  tha  baat 
original  copy  availabia  for  filming.  Faaturaa  of  thia 
copy  which  may  ba  bibliographically  uniqua, 
which  may  altar  any  of  tha  imagaa  in  tha 
raproduction.  or  which  may  significantly  changa 
tha  usual  mathod  of  filming,  ara  chackad  balow. 


ry^  Colourad  covara/ 

I I    Couvartura  da  coulaur 

□   Covers  damagad/ 
Couvartura  andommagte 


D 


D 


0 
D 


D 


Covars  raatorad  and/or  laminatad/ 
Couvartura  raataurte  at/ou  palliculte 


□   Covar  titia  missing/ 
La 


titra  da  couvartura  manqua 


|~~]    Colourad  mapa/ 


Cartaa  gtographiquaa  an  coulaur 


Colourad  ink  (i.a.  othar  than  blua  or  black)/ 
Encra  da  coulaur  (i.a.  autra  qua  blaua  ou  noira) 


{~~1   Colourad  plates  and/or  illuatratlons/ 


D 


Planchaa  at/ou  illuatrationa  an  coulaur 


Bound  with  othar  material/ 
RaliA  avac  d'autras  documents 


Tight  binding  may  causa  shadows  or  distortion 
along  interior  margin/ 

La  re  iiure  serrie  peut  causer  de  I'ombre  ou  de  la 
diatorsion  le  long  de  la  marge  int^rieure 

Blank  leavaa  added  during  reatoration  may 
appear  within  the  text.  Whenever  possible,  these 
have  been  omitted  from  filming/ 
II  aa  peut  que  certainaa  pagaa  blanchea  ajoutiea 
lors  d'une  reatauration  apparaiasant  dans  le  texte. 
mala,  lorsque  cela  Atait  r  ^ssible,  ces  pagaa  n'ont 
paa  iti  filmAea. 

Additional  comments:/ 
Commentairea  suppiinientairaa; 


L'Inatitut  a  microfilm^  le  meilleur  exemplaire 
qu'il  lui  a  itt  possible  de  se  procurer.  Les  details 
de  cet  exemplaire  qui  sorit  peut-Atre  uniques  du 
point  de  vue  bibliographique.  qui  peuvent  modifier 
une  image  reproduite,  ou  qui  peuvent  exiger  une 
modification  dnns  la  mAthode  normala  de  filmage 
sont  indiquis  ci-dessous. 


D 
D 
D 
0 
D 
0 
D 
D 
D 
D 


Coloured  pages/ 
Pagaa  de  couleur 

Pagaa  damaged/ 
Pages  endommagies 

Pages  restored  and/or  laminated/ 
Pages  restaur^aa  at/ou  pelliculAes 

Pages  discoloured,  stained  or  foxed/ 
Pages  dicolories.  tachaties  ou  piquies 

Pagaa  detached/ 
Pages  dAtachies 

Showthrough/ 
Transparence 

Quality  of  print  varies/ 
Qualiti  inAgale  de  I'impreaaion 

Includea  supplementary  material/ 
Comprend  du  materiel  supplAmentaire 

Only  edition  available/ 
Seule  Mition  disponible 

Pages  wholly  or  partially  obscured  by  errata 
slips,  tissues,  etc..  have  been  refilmed  to 
ensure  the  best  possible  image/ 
Lea  pages  totalement  ou  partiellement 
obacurcias  par  un  feuiilet  d'errata,  une  peiure. 
etc.,  ont  M  filmies  A  nouveau  de  fa^on  A 
obtanir  la  meilleure  image  possible. 


This  item  is  filmed  at  the  reduction  ratio  checked  below/ 

Ce  document  est  fiimi  au  taux  de  rMuction  indiquA  ci-dessous. 


10X 

14X 

18X 

22X 

26X 

30X 

y 

12X 


16X 


20X 


24X 


28X 


32X 


Th«  copy  fliin«d  h«r«  hM  b««n  r«produe«cl  thanka 
to  tha  ganaroaity  of: 

MMlical  Library 
McQit:  Univenity 
Montreal 

Tha  imagaa  appaaring  hara  ara  tha  boat  quality 
poaaibia  conaidaring  tha  condition  and  laglbility 
of  tha  original  copy  and  in  icaaping  with  tha 
filming  contract  spacificationa. 


L'axamplaira  film*  fut  raproduit  grica  i  la 
giniroaiti  da: 

MMlical  Library 
McQill  Univartity 
IMontraal 

Laa  imagaa  suhrantaa  ont  it*  raproduitaa  avac  la 
plua  grand  aoin,  compta  tanu  da  la  condition  at 
da  la  nattatA  da  I'axampiaira  film*,  at  t\ 
conformiti  avac  laa  conditiona  du  contrat  da 
fiimaga. 


Original  copiaa  in  printad  papar  covara  ara  filmad 
baginning  with  tha  front  covar  and  anding  on 
tha  laat  paga  with  a  printad  or  iliuatratad  impraa- 
aion,  or  tha  bacic  covar  whan  appropriata.  All  . 
othar  original  copiaa  ara  filmad  baginning  on  tha 
firat  paga  with  a  printad  or  iliuatratad  impraa- 
alon,  and  anding  on  tha  iaat  paga  with  a  printad 
or  iliuatratad  impraaalon. 


Laa  axamplalraa  origlnaux  dont  la  couvartura  an 
papiar  aat  imprimia  aom  fiimte  an  commandant 
par  la  pramiar  plat  at  wi  tarmlnant  aoit  par  la 
darnlAra  paga  qui  comporta  una  amprainta 
d'impraaaion  ou  d'iliuatration.  aoit  par  la  aacond 
plat,  aalon  la  caa.  Toua  laa  autraa  axamplalraa 
origlnaux  aont  filmia  an  commandant  par  la 
pramiira  paga  qui  comporta  una  amprainta 
d'impraaaion  ou  d'iliuatration  at  9n  tarmlnant  par 
la  damlAra  paga  qui  comporta  una  taiia 
amprainta. 


Tha  laat  racordad  f rama  on  aach  microficha 
ahaii  contain  tha  aymbol  «»>  (moaning  "CON- 
TINUED"), or  tha  aymbol  y  (moaning  "END"), 
whichavar  appiiaa. 


Un  daa  aymbolaa  auivanta  apparattra  aur  la 
damlAra  imaga  da  chaqua  microficha,  aalon  la 
caa:  la  aymbola  — »•  aignifia  "A  SUiVRE",  la 
aymbola  y  aignifia  "FIN". 


Mapa,  piataa,  charta,  ate.,  may  ba  filmad  at 
diffarant  raduction  ratioa.  Thoaa  too  iarga  to  ba 
antiraiy  includad  in  ona  axpoaura  ara  filmad 
baginning  in  tha  uppar  laft  hand  comar,  laft  to 
right  and  top  to  bottom,  aa  many  framaa  aa 
raquirad.  Tha  following  diagrama  illuatrata  tha 
mathod: 


Laa  cartaa,  pianchaa,  tablaaux,  ate.  pauvant  Atra 
filmte  i  daa  taux  da  rMuction  diff  Aranta. 
Loraqua  la  documant  aat  trap  grand  pour  Atra 
raproiduit  an  un  aau!  ciichi,  il  aat  filmA  A  partir 
da  I'angia  aupAriaur  gaucha,  da  gaucha  A  droita, 
at  da  Iwut  an  baa,  an  pranant  la  nombra 
d'imagaa  nAcaaaaira.  Laa  diagrammaa  auivanta 
illuatrant  la  mAthoda. 


1  2  3 


1 

2 

3 

4 

5 

6 

I 


I 


?li 


'1^ 


DR.  OM£r  4.  WOOO. 
IO*B>A4mmM.. 


THE  FIELD  OF  MONOCULAR  FIXATION  AND 
ITS  RELATION  TO  HETEROPHORIA. 


4 


R«m1  before  (he  flection  on  Ophthalmology  et  (he  forty-seventh 

Anaaal  Meellng  of  the  American  Medieal  Aisoeiation,  at 

AtlanM.  Oa..  May  6-«,  1806. 


9 


BY  CASEY  A.  WOOD,  M.D. 

'  CHICAGO. 


RXPRIHTED  FROM  THB 

JQUMHAL  OF  THE  AMERICAN  MEDICAL  A3B0CtATI0JI, 

NOVEMBER  98,  1896. 


II 


CHICAGO: 

AMSRICAN   MKDICAI.  ASSOCIATION   FRK88. 
1806. 


M 


r 


^7 


^ 


THK    FIELD    OF    MONOCl'LAR    FIXATION 

AND    ITS     RELATION    TO 

HETEROPHORIA. 


BV  CASEY  A.  WOOD,  M.D. 


So  little  is  Htiid  in  English  text-hooks  on  oplithal- 
inoloj^y  about  the  tield  of  tixntion  -  monocular'  or 
hinocular — and  so  much  space  is  given  to  it  in  that 
portion  of  foreign  works  devoted  to  physiologic  optics 
that  it  seemed  worth  while  to  bring  up  the  subject 
ft)r  discussion  here.  Wt^  are  so  concerned  in  investi- 
gating the  relations  of  the  extrinsic  ocular  muscles, 
as  they  are  engaged  in  fixing  some  ])oint  (doubtless 
the  most  imi)ortant  point)  immeduitely  in  front  of 
the  eyes,  i.e.,  at  the  center  of  the  tield  of  fixation,  that 
we  are  apt  to  lose  sight  of  tlu»  fact  that  the  fixing  of 
eccentric  objects  and  points  at  the  extreme  periphery 
of  the  field  is  also  of  great  importance.  It  should  be 
rememberetl  that  while  binocular  vision  may  be 
obtained  and  maintained  with  ease,  so  long  as  the 
object  fixed  is  directly  in  front,  this  result  is  often 
difficult  or  impossible  when  looking  obliquely  to  the 
extreme  left,  right,  up  or  down.  Not  only  is  this 
true  in  marked  paretic  conditions  of  one  or  other  of 
the  straight  or  oblitpie  muscles,  but  it  is  also  true  in 
the  so-called  insufficiencies.  In  other  words  the  usual 
tests  for  heterophoria  or  heterotropia-  the  various 
kinds  of  photometric  measurements  especially — give 
us  but  one  phase  of  the  conditions  under  which  the 
extrinsic  muscles  do,  or  fail  to  do,  their  daily  work. 

I  wish  to  confine  my  observations  to  one  of  the 
means  by  which  we  may  measure  the  excursions,  in 
all  directions,  of  eacili  eye  separately,  as  indicative  of 
the  pari  which  eccentric  excursions  play  in  the  pro- 
duction of  muscular  asthenopia. 


bft 


2 


It  is  to  Laiulolt  that  we  arc  chictly  iiulebtwl  for 
utilizing  tlu»  iit»l(l  of  tixatioii  in  practical  oplithal- 
inology.  The  monograph  written  by  Eperon  in  the 
Tv<ni(''  r(nnftlvt,  taken  in  connecti»)n  with  Aubert'H 
cliapterK  in  the  (Jraefe-SaeniiHch  Handbuch.  tell  us  in 
a  few  pagcH  al)out  all  we  know  of  this  subject. 

My  only  aiH.»logy  for  referring  to  these  fundamen- 
tal laws  of  optic  physiology  is  that  1  have  made  a  few- 
observations  which  may  Ih^  of  use  to  those  who  are 
now  pursuing  this  interesting  study. 

The  tield  of  tixation  of  an  eye  includes  all  those 
JV)ihts  which  the  eye  can  sucxjessively  fix,  the  head 
iH'itig  completely  at  rest.  The  limits  of  the  tield  rep- 
resent the  extreme  excursions  of  the  eyes  in  all 
directions.  At  least  three  metlunls  (two  objective 
and  one  subjective)  have  Iven  and  may  In?  employed 
in  making  these  measurements.  One  of  the  objtHJtive 
tests  consistsof  observing,  on  the  center  of  the  cornea, 
the  image  of  a  snudl  tiame  carried  along  the  arc  of 
the  perimeter,  just  tis  one  ilot^s  in  determining  the 
degret*  of  stfuint.  Another  plan  of  objective  ot^serva- 
tion  is  seen  in  the  ingenious  and  excellent  tropometer 
devise<l  by  Stevens  and  des<»ril)iHl  by  him  in  the 
Afindhs  ({'(H'liUsiitjnr  for  July,  ISUo.  By  means  of 
tins  all  tin*  movements  of  rotation  can  bi'  exactly 
measured. 

Tn  the  subjtM'tive  metlunl  we  utilize  the  visual 
acuity  and  the  perimeter.  The  object  is  usually  a 
letter  or  series  of  letters,  which  can  lx»  readily  changed, 
attachtnl  to  a  carrier  that  is  run  along  the  arc  uf  the 
IH*rimeter  as  in  measuring  the  tield  of  visiim. 

Owing  to  tlie  ditferent  methtxls  employtnl  by  vari- 
ous ol)8«^rvers  of  the  limits  «)f  the  nornuil  Held,  authors 
differ  somewhat  in  their  measurements.  The  follow- 
ing,  by  Landolt,  are  as  nearly  correct  as  we  can 
obtain  them: 


Directly  out..  .    .  *5o  /  ojr    <>ut  and  down. 
DircH-tly  in      .    .  45^  s^^      In  and  uu. 


[TIP 


I>ir«*ctly  down.     SAF  I  ^.^     I>own  and  in. 
Directly  up  .   .   .430^^^'      Up  and  out 

These  figures  vary  slightly  in   individuals,  but   the 


470  ^  «w 


L 


field,  authorH 


•t    jiK  we  ran 


lials,  but   the 


3 


tlirectly  inferior  au^ie  is  always  the  larj^est,  while  the 
infero- internal  is  always  the  smallest.  Tlie  eyelids, 
margins  of  the  orbit  and  bridge  of  the  nose  must 
always  atfect  the  result  of  these  measurements  just  as 
they  do  in  determining  the  extent  of  the  visual  field. 

Stevens,  after  speaking  of  the  importance  of  deter- 
mining tlie  absolute  as  well  as  the  comparative  rota- 
tion of  the  eyes,  not  only  from  side  to  side  but  up 
and  down,  says:  "We  have  had,  until  quite  recently, 
no  sufficient  means  f(jr  determining  these  rotations. 
The  judgment  which  we  may  form  by  watching  the 
rotations  is  not  to  be  relied  upon.  The  perimeter  is 
destitute  of  any  considerable  value  for  this  purpose. 
By  it  we  can  not  measure  the  downward  rotation  in 
many  casses,  for  the  pupil  buries  itself  behind  the 
lower  lid;  nor  can  it  measure  the  rotation  inward,  for 
the  nose  interferes,  and  even  the  outward,  the  only 
one  which  can  be  generally  measured,  is  not  well 
measured.' 

While  I  recognize,  in  general,  the  advantage  of 
objective  over  subjective  tests,  it  appears  to  me  that 
Dr.  Stevens'  objections  to  the  subjective  method  of 
determining  the  limits  of  the  ocular  excursions  are 
weakened  by  the  fact  that  what  we  wish  chiefly  to 
know  is  not  the  extreme  limit  of  rotation  of  the  eye 
in  various  directions  so  much  as  its  l<*nit  of  observa- 
tion. What  we  desire  to  ascertain  in  prvjtice  is  whether 
the  various  muscles,  alone  and  in  combination,  are 
capable  of  making  all  the  excursions  retiuiretl  for  the 
purpose  of  securing  and  maintaining  single  antl 
binocular  vision.  Whether  an  eye  would  be  able  to 
fix  an  object  further  to  the  right  or  left  if  the  nose 
were  removed,  or  one  higher  or  lower  if  a  projecting 
lid  or  orbital  margin  were  cut  away  is  not  of  essential 
importance. 

We  are  usually  advised,  also,  to  make  use  of  the 
candle  image  when  the  eye  is  and^lyopic  or  can  not 
read  large  type.  Now  these  are  just  the  conditions 
under  wliich  we  are  not  usually  concerned  about  the 
fixation  field.     It  is  the  e>e  that  sees  and   not  the 


\ 


wgmmm 


10 


w 


n, 


I 


r 


hlitid  t\ve  tliat  canwK  troiibh'  in  defective  oxcurHions. 
If  an  cyi'  takcH  no  part,  or  only  a  ftvhU'  part,  in  \\w 
work  of  fixation,  why  troiiblo  oufhcInm^h  at  all  al)out 
its  rotation? 

TlieHo  conHidorationH  cauHwl  \\\v  to  attem])t  to 
rnnt'dy  wluit  wtMHH  to  ho  certain  (lofectH  in  tlio  tech- 
ni(|n<'  of  (Irtorrninin^  thr  field  of  inonooular  fixation, 
as  it  iw  connnonly  applied.  So  far  as  1  know,  the 
tno8t  t^tfeetive  [ilan  employed  decidedly  superior  to 
the  old  Helt.iholtz-Berthold  method  -is  that  exhibited 
in  the  modified  Landolt  apparatus  attached  to  tlie 
McHardy  perimeter.  The  head  of  the  patient  is 
placed  in  the  primary  position  and  fixed  hy  biting  a 
ri^id  crossbar  of  hard  woikI. 

Lan^  thus  (h'soribes  the  method  of  examination: 
"The  balanced  test  object  exhibits  a  single  word  of 
two  or  three  letters  printed  with  the  smallest  type 
that  can  be  distinctly  seen  by  the  eye  under  investi- 
gation. The  patient  is  seattnl  at  the  perimeter,  directly 
facing  the  fixation  point,  with  his  head  erect  and  his 
chifi  supported  on  that  half  of  the  chin-rest  which 
brings  the  eye  that  is  about  to  be  tested  into  the 
middle  line,  opposite  the  fixation  spot.  If  the  patient 
can  not  maintain  this  position  during  the  whole  exam- 
ination, he  is  asked  to  grip  the  bar  of  the  bite-fixa- 
tion-apimratus  between  his  teeth,  which  effectually 
prevents  the  least  movement  of  the  head.  The  other 
eye  is  covered  with  a  pid  and  bandage,  or  its  lids  are 
closed  and  h.eid  down  by  the  lashes  with  the  tip  of 
the  patient's  forefinger.  The  words  in  the  test  object, 
in  the  various  sized  type,  are  now  exhibited,  and  one, 
in  the  finest  print  that  the  eye  can  read,  either  with- 
out or  with  gl'  f*8es,  is  exposed  after  the  test  object 
has  been  moved  to  the  end  of  the  perimeter  arc,  which 
is  extended  horizontally  outward.  While  the  patient, 
without  Tuoving  the  head,  turns  his  eye  to  the 
utmost  outward  toward  the  extremity  of  the  arc,  the 
obst^rver  slowly  moves  the  test  object  inward  toward 
the  fixation  point,  but  stops  directly  the  patient  can 
read  tlu>  wtml.   and  at  once  records,  in  degrees,  the 


1^ 


B 


poHiiioii    whioh^tlu'  U'h!  <>l)ji»ct  «M'(Mij)ioH  in  tlic  arc. 

*'Tho  arc  iH  now  plartnl  horizontally  inward,  tlu»  tcHt 
object  in  inovtMl  hack  a^ain  to  the  extremity  «)f  the 
arc,  a  frenli  wonl  iH  ex|K>He<l,  and  tlie  olwervation  iH 
rc|H»ate<l.  When  the  tield  of  fixation  han  been  tented 
in  tlie  horizontal  meridian,  which  iH  all  that  in  gen- 
erally iieceHHury,  the  examination  of  the  remainder  of 
the  tield  can  1h»  aHO(>rtain(*d  by  placing  the  arc  in 
each  iU)  degrees  of  the  circle,  and  recortling  the 
reHultn  on  a  tield  of  vinion  chart. 

"When  the  examination  of  one  eye  in  completed, 
the  luMul  in  Hhifttnl  t(»  the  opponite  Hide  of  the  chin 
rent  and  thes^'cond  eye  in  tented  in  the  name  manner." 

On  making  examinati«»nH  with  this  apparatiiH  I 
long  ago  noticwl  that  the  continuouH  effort  to  hold 
♦he  eye  at  itn  extremeHt  rotation,  in  ho  many  direc- 
tioiiH,  waH  excetnlingly  fatiguing  and  often  made  it 
difficult  to  complete  the  examination.  It  was  alHo 
HMnarked  that  the  renults  varied  in  the  same  individ- 
ual, and  I  feel  certain  that  thew  different  meanure- 
mentH  are  due  to  the  fatigue  incident  to  the  attempt  of 
the  eye  to  fix  an  object  whoHe  exact  {)oHition  at  the 
extremity  of  rotiition  is  unknown.  The  nystagmuH- 
like  movementH  of  the  glolH*.  after  a  numlHT  of  theH«» 
trials,  in  cjuite  iKjficeable. 

liiHtead  of  using  an  object  attached  to  the  carrier 
on  the  iM*rimeter  arm  I  have  used  an  exceedingly 
simi)le  device  whereby  the  rotation  of  the  globe  in  any 
direction  is  rapidly  and  easily  ineasunHl.  It  may  be 
UHed  by  all  |H»rsonH  who  can  read  .bieger  xii  at  fifty 
.centimeters,  and  may  even  Ix' employed  for  others 
whow  visual  acuity  at  that  dintance  in  C(m8idera!)ly 
less.  Four  strips  of  unglazinl  [)archment  pajx^r  have 
printed  on  them  words  of  two  letters  placed  l)etween, 
as  well  as  Ih'Iow,  figures  representing  the  <legre€?s  of 
latitude  on  the  i)erimeter  arc.  Tlu'W^  strips  are. 
together,  place<l  in  position  on  the  arm  of  the  peri- 
meter, the  patient's  head  iK'ing  in  the  primary  posi- 
tion ( I  usually  do  not  consider  any  elal)orate  fixation 
necessjirv  )  and  he  is  asknl  to  read  to  the  lower  line,  as 


p 


)ifH  ill  tlu»  arc. 
inward,  tliotvHt 
;trtMuity  of  tlie 
ohHorvatioii  \h 
luiH  been  tented 
all  that  in  gen- 
ie remainder  of 
UK  tlit»  arc  in 
recording    the 

'  iH  completed, 
de  of  the  chin 
Hiime  manner." 
Ik   apparatuH  1 

etfort   to  hold 

<o  numy  direc- 

often  made  it 

I.     It  waH  also 

same  individ- 
?rent  ineasun*- 
» the  attempt  of 
K>Hition  at  the 
he  nystagmus- 
inlh'r  of  these 

to  the  carrier 

n  exceedingly 

e  globe  in  any 

It  may  Int 

er  xii  at    tifty 

ed   for  others 

ccmsiderably 

it  pajKT  have 

iced  l)et\veen, 

le  degrees  of 

strips  are, 


[I 


ik 


(i 


f  the 


peri- 
primary  posi- 
orate  tixation 
lower  line,  as 


faraway  from  the  center  as  possible.  This  accomp- 
lished  lu»  is  reciuestcd  to  give  the  tigure  placed  above 
the  wonl  just  recognized  and  to  try  and  read,  farther 
(mt,  additional  letters  on  the  tigure  line.  Each  word 
beyond  represents  about  one  degn^e  on  the  scale  and 
the  nund)er  of  words  so  read  added  to  the  previous 
Hgure  gives  tlu'  limit,  in  degrees,  of  the  Held  in  that 
direction.  As  tach  quadrant  of  the  circle  is  passed 
over,  a  slip  of  paper  is  removed,  revealing  the  next 
paper  wlu)se  lettering,  being  different,  suggests 
nothii»g  to  the  person  under  examimition.  I  have 
found  that  instead  of  making  the  vertical  letters 
face  up  and  down  one  can  accomplish  the  purpose 
of  distinct  visitm  by  printing  them  with  type  of 
a  bolder  face,  thus  providing  for  those  rare  castas  in 
which  it  is  desired  to  test  the  muscles  (»f  an  eye 
that  can  not  read  Jaeger  xii,  or  thereabouts. 

My  investigations  of  the  tield  of  tixation  have 
developed  nothing  new  except  that  the  normal  tield, 
in  persons  wlujse  view  is  not  cut  off  by  the  nose, 
lids  or  orbital  margin«,  seems  to  have  wider  limits 
than  those  set  down  by  Lmidolt,  particularly  in  the 
downward  direction. 

The  causes  that  detenu ine  an  unusual  shape  or 
abnornud  position  of  the  whole  tield,  as  pictured  on 
the  perimetric  chart  are.  commonly,  actual  paresis  of 
one  or  more  of  the  external  muscles  of  the  eye.  Apart 
from  an  abnonnal  contiguration  of  the  face,  we  also 
recognize  those  inHuences  that  underlie  the  various 
forms  of  heterophoria,  /.  f.,  general  fatigue,  weariness 
of  one  or  more  (jf  the  extrinsic  muscles,  age,  defective 
innervation  and,  possibly,  congenital  defects  in  the 
muscular  tiben^  Hut  in  cases  of  heterophoria  occur- 
ring during  the  Hxatiim  of  objects  directly  in  front  of 
the  eye,  the  state  of  the  refniction  exerts  a  very  wide 
influence,  on  the  size,  shape  and  situation  of  the  whole 
tield.  Its  boundaries  are  enlarged  in  moderate  degrees 
of  hyperopia,  but  are  diminished  in  the  higher  grades, 
owing,  as  Landolt  thinks,  to  the  developed  nmscles 
acting  on  a  not  too  large  globe  in  the  former  instance 


Tf 


8 


Hiid  to  the  Inck  of  development,  in  the  hitter  cnse, 
ntfec'ting  the  muscular  elements  in  common  with  all 
other  parts  of  the  eye.  It  is  restricted  in  the  ehmgated 
and  enlarged  glol)e  of  the  extreme  myope,  owing 
mainly  to  the  greater  size  of  the  eye  and  the  weakness 
due  U)  \hv  stretching  of  the  muscles. 

My  former  assistant,  Dr.  T.  A.  Wocxlruff,  and  I 
have  carefully  measured  a  large  number  of  tields,  nor- 
mal and  abnormal,  in  jx^rsons  of  all  ages  and  all  states 
of  health  and  refraction,  and  I  feel  justified  in  think- 
ing that  when  carefully  done,  using  the  device  I  have 
just  described,  the  defective  excursions  and  often  the 
defective  muscle  or  muscles  can  be  readily  detected  by 
a  glance  at  the  ix»rimeter  chart.  Take  for  example  a 
case  of  simple  left  hyperphoria  of  4  pr.  diopters. 
Here  one  obtains  a  jwrimetric  picture  whose  irregular 
outline  covern  ))erhaps,  as  much  ground  as  the  nor- 
mal field  but  whost^  directly  upwanl  and  downward 
limits  in  the  left  eye  are  higher  than  normal.  Thus 
we  have  not  only  an  indication  of  the  amount  nnd 
kind  of  the  heterophoria  but  we  are  enabled,  by  a 
comparison  with  the  normal  field,  to  arrive  at  a  con- 
clusit>n  not  oidy  as  to  the  actual  direction  of  the 
muscular  deftH»t  but,  als<j,  in  some  cases,  to  venture  a!i 
opinion  as  to  particular  muscle  or  muscles  involved. 


-     ,)-  ** 


*^ 


^.-1.^,,_-  , , 


the  latter  case, 
uinmon  with  all 
in  the  elongated 

myope,  owiiig 
nd  the  weakness 

VoodruflF,  and  I 
)er  of  fields,  nor- 
?8  and  all  states 
stifled  in  think- 
le  device  I  have 
s  and  often  the 
Jily  detected  by 
3  for  example  a 

4  pr.  diopters, 
whose  irregular 
nd  as  the  nor- 
and  downward 
normal.  Thus 
le  amount  and 

enabled,  by  a 
irrive  at  a  con- 
reotion  of  the 
-5,  to  venture  an 
scles  involved. 


1 


